1. Technical Field of the Invention
This invention relates to screen systems located in fluid conduits such as waste water treatment streams, power plants, sewers, and cooling water streams. More particularly, this invention refers to a bar screen system with emergency discharge doors to prevent the fluid from overflowing should the grid screen become obstructed.
2. Description of the Prior Art
Bar screens are used for screening solids and debris from flowing liquids streams. An example of such a bar screen system can be found in U.S. Pat. No. 5,730,862 issued to Mahr. In such systems, the bar screen typically comprises a series of rakes that pass over a series of parallel screen bars, which make up a grid screen, and removes the debris collected from the flowing stream. Occasionally, large pieces of debris can block the grid screen and cause fluid to flow over the top of the screen system and the banks of the channel in which the screen system is installed.
Systems, such as the screen in the Mahr Patent, have tried to deal with the problem by using nozzles to spray the debris off of the rakes and grid screen or either reversing the direction of travel for the rakes until the impediment has been removed from the grid screen. However, these attempts are not always successful at clearing the grid screen enough to continue operation of the screen system, especially when the debris is relatively large in size.
A need exists for a screen system that will prevent fluid from flowing over the screen system and channel banks in the event of blockage in the grid screen. Ideally, such a system should be capable of being adapted to the specific fluid applications and also be able to be used on existing screen system equipment with minimal modification.
This invention provides a novel apparatus and method for preventing fluid from flowing over the top of a bar screen system. Debris and other solids can obstruct the fluid flow through the bar screen system. The bar screen system of the present invention is equipped with emergency discharge doors to prevent fluid from overflowing should the grid screen become obstructed.
The invention generally comprises a screen frame, which has a front edge and a rear edge. The rear edge is attached to a debris plate and a grid screen, which is located below the debris plate. The grid screen comprises a plurality of vertical, flat bars and a plurality of rakes that contain fingers that fit between the vertical, flat bars and clean off debris. The rakes are attached to chains on both rake ends in order for the rakes to travel over the distance of the screen system. The chains are driven by a motor.
The improvement to the screen systems of prior art is the inclusion of emergency discharge doors located on the debris plate above the grid screen. The emergency discharge doors can be manually or remotely opened with handles. The emergency discharge doors can also include a mechanism, which is described in greater detail below, to free the doors to where they can fall freely due to the weight of the water. The doors are needed when there is an obstruction in the grid screen that the rakes cannot clear and causes a blockage in the fluid flow. Since the fluid cannot pass through the grid screen, the fluid builds up in front of the grid screen and debris plate. If the debris is not removed from the grid screen, then the fluid will eventually flow over the top of the screen and sides of the fluid channel.